Homogeneous Distribution of 26Al in the Solar System from the Mg Isotopic Composition of Chondrules

The timing of the formation of the first solids in the solar system remains poorly constrained. Micrometer-scale, high-precision magnesium (Mg) isotopic analyses demonstrate that Earth, refractory inclusions, and chondrules from primitive meteorites formed from a reservoir in which short-lived aluminum-26 (Al-26) and Mg isotopes were homogeneously distributed at +/- 10%. This level of homogeneity validates the use of Al-26 as a precise chronometer for early solar system events. High-precision chondrule Al-26 isochrons show that several distinct chondrule melting events took place from similar to 1.2 million years (My) to similar to 4 My after the first solids condensed from the solar nebula, with peaks between similar to 1.5 and similar to 3 My, and that chondrule precursors formed as early as 0.87(-0.16)(+0.19) My after.